But will they be able to reach an agreement, and will it be enough to prevent irreversible damage if they do?

An estimated 7000 people marched in Wellington to the steps of Parliament, demanding more action to address climate change, on Saturday. Photo: RNZ / Johnny Blades

Climate change - what causes it

Gases in the atmosphere trap heat that radiates from the surface of the Earth, causing warmer temperatures.

Global warming is expected to raise sea levels. Photo: 123rf

The increased concentration of greenhouse gases has largely been driven by human activity, mainly the burning of fossil fuels.

The Ministry for the Environment and Statistics New Zealand released a state of the environment report last month - Environment Aotearoa 2015 - which showed New Zealand's greenhouse gas emissions increased 42 percent between 1990 and 2013.

The five biggest contributors to this were carbon dioxide from road transport and electricity generation (from coal and gas), nitrous oxide from agricultural soils, hydrofluorocarbons from industrial and household refrigeration and air conditioning systems, and methane from farm animals.

New Zealand's greenhouse gas emissions in 2013 (by sector, in million tonnes of CO2 equivalent). Graphic: Ministry for the Environment

The agriculture sector is the largest contributor to New Zealand's greenhouse gas emissions, making up 48 percent in the 13-year period.

The emissions from agriculture are mainly methane from animals and nitrous oxide from fertiliser in soils. Methane and nitrous oxide do not stay in the atmosphere as long as carbon dioxide, but they retain more heat.

Prime Minister John Key is in Paris for the talks. Photo: RNZ

The energy sector, which includes electricity generation and road transport, is the country's second-biggest emitter, contributing 39 percent of emissions between 1990 and 2013.

Emissions from electricity generation can fluctuate depending on how much rain falls, because New Zealand's energy is largely driven by hydro. When hydro inflows are low because of a lack of rain, energy is generated from other sources such as coal and gas.

It can also be influenced by economic conditions; a downturn will reduce the number of trucks out on the road.

Emissions from industrial processes and the products New Zealanders use contributed 6 percent. This included hydrofluorocarbons used in industrial and household refrigeration and air-conditioning systems, and carbon dioxide from mineral, chemical and metal production.

The waste New Zealanders produced, including landfill waste and industrial and domestic wastewater, made up the final 6 percent of the country's emissions profile.

What is being done about it?

The conference in Paris, which is expected to attract 50,000 people over two weeks, is expected to be a make-or-break moment. Countries are being urged to agree on a binding deal on emissions that would restrict global warming to no more than 2°C above pre-industrial levels.

If they don't then irreversible climate change damage, including the melting of Greenland's ice sheet and an outpouring of greenhouse gases from permafrost thawing, could occur.

To reach the target would require a cut in emissions of between 40 and 70 percent over the next 35 years.

The New Zealand government announced in July a target of reducing emissions to 30 percent below 2005 levels by 2030, which is another way of saying an 11 percent reduction on 1990 levels.

New Zealand's target has been slammed as "inadequate" by Climate Action Tracker, which produces independent scientific analysis by four research organisations,

If most other countries followed the New Zealand approach, global warming would exceed 3-4°C, the tracker report said.

Scientists say the higher the warming, the greater and more severe extreme weather events will become; sea levels will rise, along with the number of climate refugees and threats to food security and biodiversity.

If no effort is made to reduce emissions, temperatures could rise by as much as 4.8° by the end of the century, according to the Intergovernmental Panel on Climate Change.

The COP21 conference gets underway on Monday morning in France (Monday evening in New Zealand).